This invention relates to piston ring locators which are intended to position a split piston ring so that the ring will not rotate in the groove during operation of the engine.
It is important, particularly in two-stroke internal combustion engines, to prevent the split piston ring from rotating to a radial position where the ends of the ring are exposed to the exhaust port or the transfer port. Such exposure permits one or both of the ring ends to expand radially outwardly into the port and to be broken off or jammed as the piston is driven from the port.
A variety of techniques have been proposed to position the ends of the split ring in a predetermined radial position on the piston so that the ends will clear the exhaust and transfer ports. One such arrangement is disclosed in U.S. Pat. No. 5,664,536 to Bigsby. In that patent, the piston ring groove is machined so that a recess extends radially inward from a portion of the groove. A split piston ring is located in the groove and the ring is provided with a tab which extends radially inward and is received within the recess, thereby preventing rotation of the ring relative to the piston.
Other piston ring locating techniques are demonstrated in U.S. Pat. Nos. 2,481,552 and 2,481,553 to Williams. Both of these patents provide an annular channel machined into the piston ring groove. A wire locking clip is placed in the channel so that it is located inwardly of the piston ring. In both patents, one end of the wire clip is bent radially outwardly and cooperates with a hole drilled through the ends of the split piston ring. The piston ring is anchored in position according to the teachings of the ""552 patent by frictional engagement of the wire within the channel. The piston is anchored in position according to the teachings of the ""553 patent by an in-turned end portion of the wire which comprises an anchoring stud. The anchoring stud is received in a hole drilled radially into the piston.
A common technique for locking a split piston ring against rotation is to drill and ream a small hole radially into the bottom of the piston ring groove. A steel pin is press fitted into the hole. An abutment pocket is formed at the ends of the split piston ring and the pin is received in the pocket to prevent rotation of the ring.
These prior art techniques add to the cost of the piston because of the additional precision machining operations on the piston and/or piston ring. Further, stop pins embedded in the piston tend to loosen or break during prolonged operation.
This invention overcomes many of these prior art problems by providing a piston and piston ring assembly having a low-cost piston ring locator which is reliable and which does not require costly modifications to the piston and/or piston ring.
According to the invention, the assembly includes a piston having a circumferential piston ring groove defined by an axially extending circumferential bottom wall and spaced radially extending annular sidewalls. A split piston ring is located in the groove together with a piston ring locator. The locator is a flattened steel wire in the form of a ring-shaped clip having an annular body portion and first and second end portions. The clip is sandwiched between the piston ring and one of the groove sidewalls. A first segment of the clip is displaced and extends substantially in a first axial direction. A second segment of the clip is displaced and extends substantially in a second axial direction. A notch is provided in one of the groove sidewalls and extends in one of the axial directions and the ends of the split ring form an abutment pocket extending in another one of the axial directions. The first segment of the clip is received in the notch and the second segment of the clip is received in the abutment pocket to thereby lock the ring against any substantial movement relative to the piston.
According to one aspect of this invention, the first segment of the clip is the first of the end portions and the second segment of the clip is in the annular body portion.
According to a further aspect of this invention, the first segment of the clip is the first of the end portions and the second segment of the clip is the second of the end portions.
According to another aspect of this invention, the first segment of the clip is in the annular body portion and the second segment of the clip is in the annular body portion.
According to a still further aspect of this invention, the first segment of the clip is in the annular body portion and the second segment of the clip is the second of the end portions.
It will become apparent that this invention does not involve precision machining or forming operations on the piston and/or the piston ring, nor the placement of a stud or pin in the piston to restrain rotation of the ring.